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package wire
import (
"crypto/rand"
"encoding/binary"
"errors"
"github.com/quic-go/quic-go/internal/protocol"
)
// ParseVersionNegotiationPacket parses a Version Negotiation packet.
func ParseVersionNegotiationPacket(b []byte) (dest, src protocol.ArbitraryLenConnectionID, _ []protocol.Version, _ error) {
n, dest, src, err := ParseArbitraryLenConnectionIDs(b)
if err != nil {
return nil, nil, nil, err
}
b = b[n:]
if len(b) == 0 {
//nolint:staticcheck // SA1021: the packet is called Version Negotiation packet
return nil, nil, nil, errors.New("Version Negotiation packet has empty version list")
}
if len(b)%4 != 0 {
//nolint:staticcheck // SA1021: the packet is called Version Negotiation packet
return nil, nil, nil, errors.New("Version Negotiation packet has a version list with an invalid length")
}
versions := make([]protocol.Version, len(b)/4)
for i := 0; len(b) > 0; i++ {
versions[i] = protocol.Version(binary.BigEndian.Uint32(b[:4]))
b = b[4:]
}
return dest, src, versions, nil
}
// ComposeVersionNegotiation composes a Version Negotiation
func ComposeVersionNegotiation(destConnID, srcConnID protocol.ArbitraryLenConnectionID, versions []protocol.Version) []byte {
greasedVersions := protocol.GetGreasedVersions(versions)
expectedLen := 1 /* type byte */ + 4 /* version field */ + 1 /* dest connection ID length field */ + destConnID.Len() + 1 /* src connection ID length field */ + srcConnID.Len() + len(greasedVersions)*4
buf := make([]byte, 1+4 /* type byte and version field */, expectedLen)
_, _ = rand.Read(buf[:1]) // ignore the error here. It is not critical to have perfect random here.
// Setting the "QUIC bit" (0x40) is not required by the RFC,
// but it allows clients to demultiplex QUIC with a long list of other protocols.
// See RFC 9443 and https://mailarchive.ietf.org/arch/msg/quic/oR4kxGKY6mjtPC1CZegY1ED4beg/ for details.
buf[0] |= 0xc0
// The next 4 bytes are left at 0 (version number).
buf = append(buf, uint8(destConnID.Len()))
buf = append(buf, destConnID.Bytes()...)
buf = append(buf, uint8(srcConnID.Len()))
buf = append(buf, srcConnID.Bytes()...)
for _, v := range greasedVersions {
buf = binary.BigEndian.AppendUint32(buf, uint32(v))
}
return buf
}
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